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Kale

What's New and Beneficial About Kale

Among all 100 of our WHFoods, kale tops the list in terms of lutein content. Kale is not only our most lutein-rich food at WHFoods, it is also the top lutein-containing food in the USDA's National Nutrient Database that analyzes 5,350 foods that contain this carotenoid nutrient. Among the carotenoids, lutein is perhaps best known for its supportive role in eye health, and in particular, for its ability to protect different parts of the eye from potential damage by light or oxygen. A recent study on African-American women has shown decreased likelihood of glaucoma (an eye problem usually caused by increased pressure within the eye) when dietary intake of kale reaches higher intake levels. In this case, "higher intake levels" were defined as any levels exceeding at least one half-cup serving per week. Since our WHFoods serving size for kale is one cup, you will be getting more than this amount from one serving based on our standard. Among all of the vegetables examined in this particular study, kale and collards came out at the top of the vegetable list in this study for decreasing the likelihood of glaucoma!

A recent study has analyzed the combination of kale with lentils and found this food combination to be especially complementary in providing us with nutrient-richness. Interestingly, this study focused on two areas of nutrition: mineral nourishment and "prebiotic nutrients." Prebiotic nutrients are nutrients that support the growth of desirable bacteria within our digestive tract. These nutrients often involve short chains of simple sugars called "oligosaccharides." (Glucooligosaccharides, fructooligosaccharides, and xylooligosaccharides are well-studied examples of oligosaccharides.) In this study, researchers determined that the combination of prebiotic nutrients in kale-plus-lentils and the combination of mineral nutrients in kale-plus-lentils were especially were especially complementary as each food provided the nutrients that the other one lacked. In each nutrient category, kale and lentils were able to "bring something special to the table" that the other could not, resulting in outstanding combined nutrient richness. Why not take advantage of this unique food combination by starting with our Curried Lentils? Each serving of this vegetarian entreé will provide you with 1/2 cup of kale and 1/2 cup of lentils.

The research track record for kale in providing overall cardiovascular support is fairly strong, and not limited to improvement in blood cholesterol levels. However, research on kale and cholesterol levels is especially interesting. Recent studies show that kale can provide you with some special cholesterol-lowering benefits if you cook it by steaming. The fiber-related components in kale do a better job of binding together with bile acids in your digestive tract when they've been steamed. When this binding process takes place, it's easier for bile acids to be excreted, and the result is a lowering of your cholesterol levels. Raw kale still has cholesterol-lowering ability—just not as much. Along these same lines, a recent study has examined the impact of 5 ounces of kale juice per day for 12 weeks in men with high blood cholesterol levels (above 200 mg/dL). Consumption of kale juice was determined to raise the HDL levels in these study participants, lower their LDL levels, and also improve their atherogenic profiles (which measured their likelihood of developing coronary artery disease). At WHFoods, we always encourage consumption of whole foods in their minimally processed forms. However, we also believe that this study on kale juice underscores the remarkable health benefits that can be derived from this cruciferous vegetable.

Recent genetic studies on kale have shown it to have remarkable diversity, not only in terms of its physical varieties but also in terms of its nutrient content. For example, over 45 different flavonoids are known to be present in significantly differing amounts across the many different varieties of kale that can be found within the very broad kale family. One recent study has compared an Italian Lacinato-type variety of kale (also sometimes called Tuscan Black or Dinosaur kale) to a North American broad-leafed kale (often called a Napus or Siberian type kale) as well as to a German curly-leaf variety of kale (belonging to the Scotch/Scotch-Curled type of this cruciferous vegetable). As you can see, the very description of these kale types requires us to think about two continents and even more countries in which the kale was being grown. This particular study focused on sulfur-containing compounds in kale—including its glucosinolates. The researchers determined that glucosinolate content in kale can vary by as much as 10-fold depending on the specific variety in question and the conditions of cultivation and harvest. In general, this study showed that curly-leafed kale varieties and darker Lacinato varieties of kale contained higher levels of glucosinolates (and especially one particular glucosinlate called glucoraphanin) than the broad-leafed, Napus/Siberian types of kale. For glucosinolate-related health benefits from kale, you might want to focus on these varieties. In our Description section, you can find more details about each of these kale varieties.

Kale is now recognized as providing comprehensive support for the body's detoxification system. New research has shown that the ITCs made from kale's glucosinolates can help regulate detox at a genetic level.

WHFoods Recommendations

You'll want to include kale as one of the cruciferous vegetables you eat on a regular basis if you want to receive the fantastic health benefits provided by the cruciferous vegetable family. At a minimum, we recommend 3/4 cup of cruciferous vegetables on a daily basis. This amount is equivalent to approximately 5 cups per week. A more optimal intake amount would be 1-1/2 cups per day, or about 10 cups per week. You can use our Veggie Advisor for help in figuring out your best cruciferous vegetable options.

Kale is one of the healthiest vegetables around and one way to be sure to enjoy outstanding nutrition and flavor from kale is to cook it properly. We recommend Healthy Steaming kale for 5 minutes. To ensure quick and even cooking cut the leaves into 1/2" slices and the stems into 1/4" lengths. While there might be potential health benefits from letting the stems and slices sit for about 5 minutes prior to cooking, the scientific research in this area is definitely mixed. You can find many key details in our article, Can Preparation Methods Impact the Benefits of Cruciferous Vegetables?.

This chart graphically details the %DV that a serving of Kale provides for each of the nutrients of which it is a good, very good, or excellent source according to our Food Rating System. Additional information about the amount of these nutrients provided by Kale can be found in the Food Rating System Chart. A link that takes you to the In-Depth Nutritional Profile for Kale, featuring information over 80 nutrients, can be found under the Food Rating System Chart.

Health Benefits

While not as well researched as some of its fellow cruciferous vegetables like broccoli or cabbage, kale is a food that you can count on for some outstanding health benefits, if for no other reason than its exceptional nutrient richness. In our own website food rating system, kale scored 5 excellents, 6 very goods, and 8 goods—for a total of 19 standout categories of nutrient richness! That achievement is difficult for most foods to match.

Antioxidant-Related Health Benefits of Kale

Like most of its fellow cruciferous vegetables, kale has been studied more extensively in relationship to cancer than any other health condition. This research focus makes perfect sense. Kale's nutrient richness stands out in three particular areas: (1) antioxidant nutrients, (2) anti-inflammatory nutrients, and (3) anti-cancer nutrients in the form of glucosinolates. Without sufficient intake of antioxidants, our oxygen metabolism can become compromised, and we can experience a metabolic problem called "oxidative stress." Without sufficient intake of anti-inflammatory nutrients, regulation of our inflammatory system can become compromised, and we can experience the problem of chronic inflammation. Oxidative stress and chronic inflammation—and the combination of these metabolic problems—are risk factors for development of cancer. We've seen research studies on five specific types of cancer—including bladder cancer, breast cancer, colon cancer, ovarian cancer, and prostate cancer—and intake of cruciferous vegetables (specifically including kale). As a group, these studies definitely show cancer preventive benefits from kale intake, and in some cases, treatment benefits as well.

Kale's cancer preventive benefits have been clearly linked to its unusual concentration of two types of antioxidants, namely, carotenoids and flavonoids. Within the carotenoids, lutein and beta-carotene are standout antioxidants in kale. As mentioned in our What's New and Beneficial section, over 45 different flavonoids have been identified in kale. Most prominent among kale's flavonoids are its flavonols, including kaempferol, quercetin, and isorhamnetin. Researchers have actually followed the passage of these two carotenoids in kale from the human digestive tract up into the blood stream, and they have demonstrated the ability of kale to raise blood levels of these carotenoid nutrients. That finding is important because lutein and beta-carotene are key nutrients in the protection of our body from oxidative stress and health problems related to oxidative stress. Increased risk of cataracts, glaucoma, atherosclerosis, and chronic obstructive pulmonary disease (COPD) are four such problems. Also among these chronic health problems is cancer since our overall risk of cells becoming cancerous is partly related to oxidative stress.

Within the flavonoids, kaempferol is a spotlight antioxidant in kale, followed by a flavonoid called quercetin. You're likely to be getting about 60 milligrams of kaempferol in the one-cup serving of kale that we use as the standard serving size on our website, as well as 29 milligrams of quercetin. Alongside of these spotlight flavonoids, however, it is probably the very broad spectrum of flavonoid antioxidants in kale that are largely responsible for kale's cancer-preventive and other benefits, owing to their ability to reduce oxidative stress.

Anti-Inflammatory Health Benefits of Kale

We have yet to see research on kale's omega-3 content and inflammation, but we would expect this kind of research to show the omega-3s in kale to be an important part of kale's anti-inflammatory benefits. It only takes 100 calories of kale to provide over 350 milligrams for the most basic omega-3 fatty acid (alpha-linolenic acid, or ALA). We suspect that this amount will be plenty to show direct anti-inflammatory benefits from routine kale intake.

We also have yet to see specific research on inflammation and kale's vitamin K content. But we know that kale is a spectacular source of vitamin K (one cup of kale provides far more micrograms of vitamin K than any of our World's Healthiest foods) and we also know that vitamin K is a key nutrient for helping regulate our body's inflammatory process. Taken in combination, we expect these two facts about vitamin K to eventually get tied together in health research that shows kale to be an exceptional food for lowering our risk of chronic inflammation and associated health problems.

Glucosinolates and Cancer-Preventive Benefits of Kale

What we have already seen in the health research on kale is ample evidence that its glucosinolates provide cancer-preventive benefits. Kale is a top food source for at least four glucosinolates, and once kale is eaten and digested, these glucosinolates can be converted by the body into cancer preventive compounds. Kale's glucosinolates and the ITCs made from them have well-documented cancer preventive properties, and in some cases, cancer treatment properties as well. At the top of the cancer-related research for kale are colon cancer and breast cancer, but risk of bladder cancer, prostate cancer, and ovarian cancer have all been found to decrease in relationship to routine intake of kale. The chart below presents a summary of the unusual glucosinlate phytonutrients found in kale, and the anti-cancer ITCs made from them inside the body

Glucosinolates in kale and their detox-activating isothiocyanates

Glucosinolate

Derived Isothiocyanate

Isothiocyanate Abbreviation

glucobrassicin

indole-3-carbinol*

I3C

glucoraphanin

sulforaphane

SFN

gluconasturtiian

phenethyl-isothiocyanate

PEITC

glucopaeolin

benzyl-isothiocyanate

BITC

sinigrin

allyl-isothiocyanate

AITC

* Indole-3-carbinol (I3C) is not an isothiocyanate. It's a benzopyrrole, and it is only formed when isothiocyanates made from glucobrassicin are further broken down into non-sulfur containing compounds.

In addition to the glucosinolates listed above, scientists have also identified glucobrassicanapin, glucoiberin, and gluconapin as glucosinlates present in kale.

Kale's Cardiovascular Support

One set of health events that most people would like to avoid is clogging of the arteries (arteriosclerosis). Since plaque formation along the walls of the arteries is required for clogging, and since the plaque formation process is usually preceded by chronic inflammation and chronic oxidative stress, it is not surprising to see a food like kale lessening our risk of arteriosclerosis. The reason is simple: kale is a concentrated source of antioxidants and anti-inflammatory nutrients, as already described this Health Benefits section.

But the cardiovascular benefits of kale also extend to its cholesterol-lowering ability. What happens here is fairly straightforward. Kale contains a variety of fiber-related nutrients that can bind together with bile acids. When this binding takes place, our blood cholesterol levels go down because our body needs to replace the bile acids and they can be obtained from the breakdown of cholesterol. Studies on kale intake show that total blood cholesterol and LDL cholesterol drop with increasing amounts of kale in the diet, while interestingly, blood levels of HDL cholesterol increase. (Since higher levels of HDL cholesterol generally improve our cardiovascular health, this increase in HDL is a good thing.) Intake of both raw and steamed kale have been shown to provide cardio benefits, but the benefits seem somewhat stronger from intake of steamed kale. It's also worth noting that a recent study on kale juice (using 5 ounces per day for 12 weeks) has shown these same cholesterol-related benefits.

Other Health-Related Benefits of Kale

Kale has a definite role to play in support of the body's detoxification processes. The isothiocyanates (ITCs) made from kale's glucosinolates have been shown to help regulate detox activities in our cells. Most toxins that pose a risk to our body must be detoxified by our cells using a two-step process. The two steps in the process are called Phase I detoxification and Phase II detoxification. The ITCs made from kale's glucosinolates have been shown to favorably modify both detox steps (Phase I and Phase II). In addition, the unusually large numbers of sulfur compounds in kale have been shown to help support aspects of Phase II detoxification that require the presence of sulfur. By supporting both aspects of our cellular detox process (Phase I and Phase II), nutrients in kale can give our body an "edge up" in dealing with toxic exposure, whether from our environment or from our food.

We have yet to see studies that look directly at kale and its support for our digestive system. However, we have seen studies for kale's fellow cruciferous vegetable—broccoli—in this regard, and we definitely expect to see future research that looks directly at kale and our digestive function. We predict that one area of digestive support provided by kale will turn out to involve fiber. We feel that 7 grams of fiber per 100 calories of kale is just too much fiber to fail in the digestive benefits category. And researchers have already identified the presence of key lignans—including lariciresinol and pinoresinol—in kale. (For pinoresinol, the levels in raw curly kale average about 220 milligrams in our WHFoods one-cup serving size.) Lignans are classified as polyphenols, and not fibers. So the connection between kale lignans, kale fiber content, and digestive support is indirect. But scientists do know that lignins—the much larger molecules that have a direct relationship with fibers like cellulose and hemicellulose mdash;can contain lignans including the pinoresinol and lariciresinol found in kale. So there is very likely to be a fiber-related and digestion-supportive role played by these kale lignans.

We predict that a second area of digestive benefits will involve kale's glucosinolates. The ITCs make from kale's glucosinolates should help protect our stomach lining from bacterial overgrowth of Helicobacter pylori and should help avoid too much clinging by this bacterium to our stomach wall.

Description

Kale is a remarkable member of the cruciferous vegetable family known for its ability to thrive during the cooler seasons of the year and its tendency to grow wild on many different continents, and especially in countries bordering along the Mediterranean Sea. The cool-season nature of kale can sometimes be reflected in its flavor. When exposed to frost, kale can sometimes take on a sweeter taste (that is due to the conversion of some kale starches into sugars). Overall, however, the taste of kale can be surprisingly varied, from bitter or peppery to more plain and slightly sweet.

The three types of kale that we have become familiar with in the produce section of today's grocery stores are actually domesticated versions of wild plants that took farmers hundreds of years to develop. These three types include (1) flatter, wider-leafed kale, (2) darker Lacinato-type kale, and (3) more tightly formed, curly leafed kale. The list below shows some common kale varieties belonging to each of these three types:

Of course, there are not always sharp dividing lines between these three types of kale, and you can expect to find varieties that blend different features. Regardless of variety, however, all versions of kale are considered cruciferous vegetables and belong to the Brassica genus of plants that also includes bok choy, broccoli, Brussels sprouts, cabbage, cauliflower, collards, mustard greens, and turnip greens.

You can find different colors of kale in all three categories described above. However, the most common leaf colors are light to dark green and lavender to dark purple. You'll also find green-leafed kale with purple stems and veins. All of the kales discussed thus far fall into the general category of "culinary kales" that are intended to be eaten. "Ornamental kales" are also edible, but since they have been developed primarily for appearance rather than taste or texture, they may be tougher in texture and harsher in taste.

Unfortunately from a science perspective, there is not always a guaranteed connection between the genus/species/subspecies of kale plant and the looks of the leaves as described above. However, the most common genus/species types of kale are Brassica oleracea and Brassica napus. The most common subspecies (ssp.) and varieties (var.) are:

Brassica oleracea ssp. Acephala group

Brassica oleracea var. sabellica

Brassica oleracea var. palmifolia

Brassica oleracea var. ramosa

Brassica oleracea var. costata

B. napus ssp. napus var. pabularia

Along with broccoli, Brussels sprouts, cabbage, cauliflower, and kohlrabi, you might also hear kale being referred to as a "cole crop." In general, this term refers to foods found in the Brassica oleracea genus/species of plant, and it comes from the Latin word "caulis" meaning "stem."

History

Kale as we know it today was first cultivated in the Mediterranean region over 2,000 years ago. It played an important role in the food supply of Europe through the time of the Roman Empire and during the medieval period in Europe between the 5th and 15th centuries. European colonizers are believed to have brought the first kale to North America in the 1600's, and Russian traders are believed to have first brought this vegetable to Canada a century or so later.

Several thousand farms in the United States grow kale on a commercial basis, primarily in California, Georgia, New Jersey, and Texas. Compared with its fellow cruciferous vegetable, broccoli, total kale acreage is low, and between 5,000-7,500 acres. (For comparison, broccoli acreage is noted to be 130,000-150,000 acres.)

How to Select and Store

Look for kale with firm, deeply colored leaves and moist hardy stems. Kale should be displayed in a cool environment since warm temperatures will cause it to wilt and will negatively affect its flavor. The leaves should look fresh, be unwilted, and be free from signs of browning, yellowing, and small holes. Choose kale with smaller-sized leaves since these will be more tender and have a more mild flavor than those with larger leaves. Kale is available throughout the year, although it is more widely available, and at its peak, from the middle of winter through the beginning of spring.

At WHFoods, we encourage the purchase of certified organically grown foods, and kale is no exception. Repeated research studies on organic foods as a group show that your likelihood of exposure to contaminants such as pesticides and heavy metals can be greatly reduced through the purchased of certified organic foods, including kale. In many cases, you may be able to find a local organic grower who sells kale but has not applied for formal organic certification either through the U.S. Department of Agriculture (USDA) or through a state agency. (Examples of states offering state-certified organic foods include California, New York, Oregon, Vermont, and Washington.) However, if you are shopping in a large supermarket, your most reliable source of organically grown kale is very likely to be kale that displays the USDA organic logo.

To store, place kale in a plastic storage bag removing as much of the air from the bag as possible. Store in the refrigerator where it will keep for 5 days. The longer it is stored, the more bitter its flavor becomes. Do not wash kale before storing because exposure to water encourages spoilage.

Here is some background on why we recommend refrigerating kale. Whenever food is stored, four basic factors affect its nutrient composition: exposure to air, exposure to light, exposure to heat, and length of time in storage. Vitamin C, vitamin B6, and carotenoids are good examples of nutrients highly susceptible to heat, and for this reason, their loss from food is very likely to be slowed down through refrigeration.

Tips for Preparing and Cooking

Tips for Preparing Kale

Rinse kale leaves under cold running water. Chop leaf portion into 1/2" slices and the stems into 1/4" lengths for quick and even cooking.

It's interesting to note that in one recent study on kale's glucosinolate content, 96% of kale's total glucosinolates were retained in the kale after blanching. Unfortunately, the authors did not specific the exact method used to blanch this cruciferous vegetable. However, it is very common in food science studies to blanch a food by placing it in boiling water very briefly, on the order of 1-3 minutes depending on the volume, type, and cut/uncut nature of the food. This exposure to boiling water is then usually followed by immediate submersion in ice water. So in general, we think about blanching as involving very brief exposure to heat. In this same study, it was interesting to note that about 60% of total glucosinolates in kale were lost after boiling for 5 minutes. While we cannot be certain about the exact times and percentages here—and we are clearly in need of further food science studies in this area—the glucosinolates in kale may be especially sensitive to total cooking time and this sensitivity may need to be factored in when choosing a kale cooking method.

As far as specific steps to take in your own kitchen, here are the steps that we recommend for making good overall trade-offs between nutrient retention, texture, and taste: fill the bottom of a steamer pot with 2 inches of water. While waiting for the water to come to a rapid boil chop greens. Steam for 5 minutes and toss with our Mediterranean Dressing and top with your favorite optional ingredients. We think you will love the deliciousness of these recipe results! For details see 5-Minute Kale.

Nutritional Profile

Our rating system shows kale to be an excellent source of vitamin K, vitamin C, vitamin A, manganese, and copper; a very good source of vitamin B6, fiber, calcium, potassium, vitamin E, and vitamin B2; and a good source of iron, magnesium vitamin B1, omega-3 fats, phosphorus, protein, folate, and vitamin B3. Over 45 different flavonoids have been identified in kale, and especially kaempferol, quercetin, and isorhamnetin. Its glucosonolates include glucobrassicin, glucoraphanin, gluconasturtiian, glucopaeolin, sinigrin, glucobrassicanapin, glucoiberin, and gluconapin. Kale also provides the lignans lariciresinol and pinoresinol.

Introduction to Food Rating System Chart

In order to better help you identify foods that feature a high concentration of nutrients for the calories they contain, we created a Food Rating System. This system allows us to highlight the foods that are especially rich in particular nutrients. The following chart shows the nutrients for which this food is either an excellent, very good, or good source (below the chart you will find a table that explains these qualifications). If a nutrient is not listed in the chart, it does not necessarily mean that the food doesn't contain it. It simply means that the nutrient is not provided in a sufficient amount or concentration to meet our rating criteria. (To view this food's in-depth nutritional profile that includes values for dozens of nutrients - not just the ones rated as excellent, very good, or good - please use the link below the chart.) To read this chart accurately, you'll need to glance up in the top left corner where you will find the name of the food and the serving size we used to calculate the food's nutrient composition. This serving size will tell you how much of the food you need to eat to obtain the amount of nutrients found in the chart. Now, returning to the chart itself, you can look next to the nutrient name in order to find the nutrient amount it offers, the percent Daily Value (DV%) that this amount represents, the nutrient density that we calculated for this food and nutrient, and the rating we established in our rating system. For most of our nutrient ratings, we adopted the government standards for food labeling that are found in the U.S. Food and Drug Administration's "Reference Values for Nutrition Labeling."
Read more background information and details of our rating system.

In-Depth Nutritional Profile

In addition to the nutrients highlighted in our ratings chart, here is an
in-depth nutritional profile for Kale. This profile includes information on a full array of nutrients, including carbohydrates, sugar, soluble and insoluble fiber, sodium, vitamins, minerals, fatty acids, amino acids and more.

Note:

The nutrient profiles provided in this website are derived from The Food Processor, Version 10.12.0, ESHA Research, Salem, Oregon, USA. Among the 50,000+ food items in the master database and 163 nutritional components per item, specific nutrient values were frequently missing from any particular food item. We chose the designation "--" to represent those nutrients for which no value was included in this version of the database.

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For education only, consult a healthcare practitioner for any health problems.

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